Process for producing high-grade metallic products from solid slags and high-grade metallic products

ABSTRACT

Process for recovering high-grade blast furnace iron or other metal from pieces of blast furnace iron or such other metal and blast furnace slag having large amounts of such blast furnace slag, by tumbling a substantial number of such pieces to achieve a constant redistribution thereof while impacting at least a substantial portion of such pieces with a high velocity, relatively small diameter shot or grit which has a hardness which is greater than the hardness of the slag, thereby abrading the impurity, while leaving the body of non-impurity substantially intact. A product comprising a large body of high-grade blast furnace iron or other metal and having a substantial number of superficial irregularities, crevices and fissures containing only a small amount of blast furnace slag adhered in said irregularities, crevices and fissures, the amount of blast furnace slag being no more than about ten percent by weight of the total product, and preferably no more than about two to three percent by weight of such product.

United States Patent [1 1 Burlingame PROCESS FOR PRODUCING HIGH-GRADEMETALLIC PRODUCTS FROM SOLID SLAGS AND HIGH-GRADE METALLIC PRODUCTSRichard D. Burlingame, Cleveland Heights, Ohio Luria Brothers & Co.,Inc., Cleveland, Ohio Filed: Nov. 2, 1973 Appl. No.: 412,119

Inventor:

[73] Assignee:

References Cited UNITED STATES PATENTS 8/1951 Turnbull 51/13 12/1955l-leckett 24l/DIG. 21 7/1963 Freeman 51/13 51 May 20, 1975 PrimaryExaminer-Donald G. Kelly Attorney, Agent, or FirmRobert S. Bramson,Esq.; James A. Drobile, Esq.

[ ABSTRACT Process for recovering high-grade blast furnace iron or othermetal from pieces of blast furnace iron or such other metal and blastfurnace slag having large amounts of such blast furnace slag, bytumbling a substantial number of such pieces to achieve a constantredistribution thereof while impacting at least a substantial portion ofsuch pieces with a high velocity, relatively small diameter shot or gritwhich has a hardness which is greater than the hardness of the slag,thereby abrading the impurity, while leaving the body of non-impuritysubstantially intact. A product comprising a large body of high-gradeblast furnace iron or other metal and having a substantial number ofsuperficial irregularities, crevices and fissures containing only asmall amount of blast furnace slag adhered in said irregularities,crevices and fissures, the amount of blast furnace slag being no morethan about ten percent by weight of the total product, and preferably nomore than about two to three percent by weight of such product.

10 Claims, 5 Drawing Figures PATENTED MAY 20 1975 SHEET 2 6F 2 PROCESSFOR PRODUCING HIGH-GRADE METALLIC PRODUCTS FROM SOLID SLAGS ANDHIGH-GRADE METALLIC PRODUCTS BACKGROUND OF THE INVENTION 1. Field of theInvention The invention relates to the field of iron and steelmaking,and the refining of other metals, and particularly relates to a processof recovering, from a blast furnace operation. high-grade metal having asubstantial amount of impurity, and then removing the impurity to allowthe metal commercially to be used.

2. State of the Art In the normal operation of iron blast furnaces,liquid iron is continuously collected in the hearth, and liquid slag issimultaneously forming and collecting as a separate, completelyimmiscible layer on top of the iron. As used herein, the term slag"means any material having a high degree of impurities. Iron slag," theprecise composition of which can vary substantially, is produced in theproduction of blast furnace iron and typically will have an approximatecomposition of 38 percent by weight of calcium oxide, 13 percent ofmagnesium oxide, 36 percent of silicon dioxide, percent of aluminumoxide, 1.5 percent of sulfur, and minor amounts of other metallicoxides.

In all iron blast furnaces, the liquid iron slag must be flushed outevery few hours. This iron slag is usually removed by allowing it toflow through a tap hole, known as a slag notch" or cinder notch," whichis located high in the blast furnace at approximately the normal levelof the slag. The molten iron slag is thus allowed to run out ofthe blastfurnace every few hours, in order to prevent accumulation of undueamounts of the slag.

However, because iron is constantly migrating through the slag layerduring the operation of the furnace, the pouring of the iron slag willresult in a concomitant loss of approximately one percent by weight ofthe total amount of iron produced by the blast furnace.

A typical blast furnace will produce approximately 3,000 tons of ironper day, and large blast furnaces may produce as much as l0,000 tons ofiron per day or more. It is therefore quite common to experience a lossof from about to 100 tons per day of iron with the removal of the ironslag from the blast furnace. Iron, with an acceptably low level ofimpurities contained therein, as is found in normal blast furnaces, hasa very substantial value. Thus, such losses of up to 100 tons of ironper day are obviously substantial and are desired to be minimized oreliminated completely.

In the common prior art process, the molten blast furnace iron slag isconveyed into one of two large, walled-in slag pits located right nextto the furnace, where it is allowed to solidify and cool. The slag pitcontains primarily slag, having, however, substantial irregular-shapedmasses of iron of widely varying size scattered throughout the slag,like raisins in a cake. Depending primarily on the quality of the rawmaterials entering the blast furnace, i.e., iron ore, coke andlimestone, the amount of iron slag produced per ton of iron will varysubstantially, and the amount of iron distributed throughout the slagpit is usually in the range from about two to five percent by weight ofthe total slag pit contents. The iron distributed through the iron slagin the slag pit is the same as the regular blast furnace iron product,having a relatively low level of impurities and high economic value, ifit can be separated adequately from the surrounding iron slag.

When the slag pit being worked is full, the slag from the blast furnaceis then channelled to the other slag pit, which is then empty, havingearlier been emptied by power shovels and trucks while the other slagpit was being filled. These power shovels and trucks are moved over tothe full pit, after a period of time has elapsed to allow solidificationof the iron slag, and the trucks are filled by the power shovels withlarge chunks of slag from the slag pit, which are transported to a slagprocessing facility, generally located nearby.

In the slag processing facility, the large chunks of slag, havingdimensions of up to several feet, are impacted by heavy wrecking balls,to crush the slag into pieces generally of up to 2 feet in maximumdimensions. In the past, when the slag processor had broken the ironpieces contained in the slag down to a size which could be accommodatedby an open hearth furnace charging pan, this iron-containing material.called blast furnace slag iron herein, was separated from the pieces oriron slag by use of an electromagnet, to be recycled to an open hearthfurnace. These blast furnace slag iron pieces, are highly variable intheir iron and iron slag content, but will frequently comprise about 60to percent of blast furnace iron, having a low sulfur content oftypically about 0.03 percent by weight, and 20 to 40 percent of ironslag, having a sulfur content of about I to 2 percent by weight.

Because of the substantial time involved in producing steel using anopen hearth furnace, due to the inherently long melting, refining andsuperheating cycle, the blast furnace slag iron pieces, which have ahigh sulfur content since there is l to 2 percent of sulfur in the slagwere still reusable, and could be used in open hearth steel production.The considerable melting and refining time inherent in the operation ofopen hearth furnaces, allowed ample opportunity for all of the sulfur tobe removed in the open hearth furnaces. Therefore, so long as openhearth furnaces were popular, no major problem was encountered inrecycling blast furnace slag iron.

However, basic oxygen furnace steelmaking is steadily replacing basicopen hearth steelmaking as the process of choice for converting blastfurnace iron to steel. It is expected that, in a relatively short periodof time, substantially all blast furnace iron in the United States willbe refined to steel by the basic oxygen furnace method. Although thebasic oxygen furnace process is vastly superior to the open hearthprocess in most ways, the basic oxygen furnace is inferior with respectto its flexibility in handling scrap metals, such as the blast furnaceslag iron pieces described above. In particular, most basic oxygenfurnace operators prefer to exclude these blast furnace slag iron piecesfrom their charges, because these pieces are usually considered to betoo high in sulfur content for optimum efficiency steelmaking, due totheir excess iron slag content. Unimproved blast furnace slag iron isnot suitable for basic oxygen furnace processing, because of therelatively short resi dence time of the iron in the basic oxygenfurnace. This residence time is usually not adequate to achievesufficient desulfurization of the relatively high sulfur content blastfurnace slag iron pieces. Therefore, in any integrated steel mill havingonly basic oxygen furnace steelmaking production, the blast furnace slagiron pieces produced from the mills blast furnace slag are commonlyaccumulated in large stockpiles as a low grade form of scrap, too goodto haul to the dump, but not good enough to charge, as is, into thesteelmaking basic oxygen furnace. This scrap has had a very low economicvalue in the past because, in addition to its unsuitability for basicoxygen steelmaking, it could not be utilized in any other sector of theferrous industries, such as in iron foundries.

The process of this invention involves the use of a shot blasting andtumbling machine, of a type well known in the art and more fullydescribed below. This machine is frequently used to clean looselyadherent sand from foundry castings. However, this use does not entailthe removal of a hard material, firmly attached to the iron, from minutefissures and crevices such as is involved in the process of thisinvention to remove almost all of the slag from blast furnace slag ironpieces.

BRIEF SUMMARY OF THE INVENTION The instant invention overcomes theshortcomings of prior art processes and products by providing a processfor recovering relatively low sulfur content, low slag content blastfurnace iron from a crude material, called blast furnace slag ironpieces, having a large amount of iron slag contained on the surfacethereof and extending from the surface thereof into the body thereofthrough cavities, fissures and the like. This process, althoughdisclosed to be utilized to remove blast furnace slag from blast furnaceslag iron pieces, may also be utilized to remove slag impurities fromother refined metals such as aluminum, zinc, copper and the like.

In the practice of the process of this invention, the slag and metalchunks are broken up into pieces, having sizes of up to a maximumdimension of about 2 or 3 feet, in order to make it possible to chargethem into conventional shot blasting machines and, when most of the slaghas been removed, to charge them into basic oxygen furnaces, electricfurnaces, iron foundry cupolas and the like, for further use of theiron. A typical piece will have a non-geometric shape and dimensions upto about 2 by 2 feet by 6 inches. However, because of the random way inwhich the slag is broken into pieces, any given slag pit will produceblast furnace slag iron pieces having a wide variety of shapes andsizes, down to as little as about one-quarter inch.

In the practice of this process, the blast furnace slag iron pieces, orpieces of other metal and slag, are first prepared into suitable sizes,by the use of wrecking balls or similar well-known techniques. Thepieces containing significant quantities of blast furnace iron or othermetal to be recovered are then separated from the other, principallyslag containing, pieces. In the case of iron, this separation may easilybe effected by the use of an electromagnet. The suitably sized piecesare then transported, as by trucks, conveyor belts, railroad cars, orthe like to the slag processing unit.

The slag processing unit is a tumbling and shot blasting machine, ofageneral type which is known in the art and commercially available. Inthis machine, the charge of slagmetal pieces, such as blast furnace slagiron, are placed in a suitable location, such as in a container, whereinthey are operated on by a conveyor, rotating and tumbling the mass ofindividual pieces about, in order to achieve a continuing redistributionof the pieces. As this continuing redistribution is taking place, thepieces on at least one face of the tumbling mass are subjected to theimpact of a continuous flow of relatively high velocity, hard pellets orsimilarly shaped particles, commonly called shot or grit. Shot isrelatively uniformly shaped, usually spherical, particles of metal,typically a relatively hard high carbon steel alloy. Grit is similar toshot, but instead of being spherical, it has facets and sharp corners.The hardness of the shot or grit must be substantially greater than thehardness of the slag, so that the shot or grit will erode the slag whenthe slag metal pieces are impacted with the high velocity shot or grit.

This shot or grit is impacted against the slag-metal pieces, using arelatively high velocity impeller, for taking large quantities of theshot or grit and impelling them against the slag-metal pieces atrelatively high velocity. This impact, occurring relativelycontinuously, while continuously redistributing the slag-metal pieces,such as blast furnace slag iron pieces, throughout the mass of suchpieces, allows the achievement of relatively uniform exposure of allsurfaces of all of the slagmetal pieces to the impact of the shot orgrit. As a result of this process, in a relatively short period of time,on the order of about 10 minutes to about l or 2 hours, a surprisinglygood removal of the slag from the pieces is achieved, not only at thesurface of each piece, but also extending substantially downwardly intomost, if not all, of the crevices and fissures in the piece. If theprocess begins with blast furnace slag iron pieces which have a slagcontent of about 20 to 40 percent by weight and a corresponding blastfurnace iron content of about 60 to percent by weight, enough slag maybe removed by this process that the final pieces will have a slagcontent as low as about 2 percent by weight.

The precise slag content of the final product can be regulated byvarying the conditions of the process, and particularly the size of theshot or grit, the amount of shot or grit used, the velocity imparted tothe shot or grit, the duration of the shot blasting process, and theextent to which the shot blasting enclosure is filled with slag-metalpieces. To a lesser extent, some of the superficial removal of slag isdependent upon the amount of tumbling of the individual pieces which isachieved by the conveyor for these pieces. However, this tumbling onlyremoves surface slag, and is definitely not capable of removinng, byitself, the slag located in fissures and crevices, which must be removedas well in order to be able to achieve a commercially valuable producthaving relatively low slag content, on the order of 10 percent by weightor preferably even less.

The product of the invention is a body of metal, blast furnace iron whenthe process is applied to blast furnace slag iron pieces, comprising anirregularly shaped body, the dimensions of which may vary within widelimits from a fraction of an inch to approximately 2 or 3 feet, andwhich has a multiplicity of surface-exposed fissures and crevicesthroughout the body, these fissures and crevices being relatively freeof slag, the individual pieces having a total slag content of up toabout 10 percent by weight and preferably no more than about 2 or 3percent by weight.

It is important to note that, because of the nature of the process, theslag which is located in deep crevices or fissures which extend to thesurface of the individual pieces is accessible to the shot or grit andcan be removed substantially completely by the impacting of shot or griton those pieces.

In the process of the invention, the shot or grit impacting the slagproduces a large quantity of relatively fine slag particles. as aresidue of the process. These particles may be utilized as a componentof Portland cement or the like in order to realize some economic valuefrom this otherwise useless slag.

OBJECTS OF THE INVENTION It is therefore an object of this invention toprovide a process for removing substantially all of the slag from piecescomprising a relatively high purity metal having substantial amounts ofslag thereon and extending deeply and tenaciously into crevices andfissures accessible to the surface of each piece.

Yet another object of this invention is to provide a process forremoving from blast furnace slag iron pieces the majority of the slag toproduce a product which has a slag content of no more than approximatelypercent by weight, and preferably no more than 2 or 3 percent by weight,

Still another object of this invention is to provide a slag removalprocess, capable of removing slag from highly irregularly shapedsurfaces of metal, which is applicable to a wide variety of metals,including iron, copper, aluminum. zinc and the like.

A still further object of this invention is to provide a metal producthaving the purity of a blast furnace metal, and having a large degree ofsurface irregularities, such as fissures and crevices, which aresubstantially free of impurities, containing no more than about 2percent by weight of the impurities.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematicrepresentation, in perspective, of a tumbling and blasting machine whichmay be utilized in the practice of the process of this invention;

FIG. 2 is a top plan view of a representative piece of blast furnaceslag iron prior to treatment by the process of the invention;

FIG. 3 is a cross-sectional view taken along 3-3 of FIG. 2;

FIG. 4 is a top plan view of the product of this invention,corresponding essentially to the raw material of FIG. 2 with a majorityof the slag removed, so that the final slag content of the product is nomore than about two percent by weight; and

FIG. 5 is a cross-sectional view, taken along line 55 of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION Viewing FIG. 2, the numeral 10generally designates a representative blast furnace slag iron piece. Thepiece illustrated, which will have a maximum dimension of approximately2 or 3 feet and a maximum thickness of approximately 6 inches, comprisesa principal continuous phase of blast furnace iron, generally designatedby the numeral 12, and an outer covering of slag, generally designatedby the numeral 14.

Viewing FIG. 3, it will be seen that the body of iron contains a largenumber of crevices and fissures, of varying depths, sizes and shapes.Many of these fissures which are generally designated by numeral 16, aresubstantially filled with varying amount of hard, tough,

tightly adhering slag.

Viewing FIG. 3, it will be seen that such portions of iron as aregenerally designated by numeral 12 are seen in FIG. 2 as being quitesmall and superficially exposed iron segments on the surface of piece10. In FIGS. 4 and 5, the final blast furnace iron product of thisinvention is generally designated by numeral 18.

It should be understood that FIGS. 2 to 5 inclusive are intended merelyto be general schematic representations of what a piece of blast furnaceslag iron may look like before and after the process of this inventionand do not correspond precisely to any given piece of material.

Pieces 10 are formed from a blast furnace when the molten slag,containing about 2 to about 5 percent of molten iron, is tapped offthrough the slag notch or cinder notch of a conventional blast furnace.That iron and slag mixture is flowed, in the molten state, into suitableslag pits, where it is allowed to harden. This pit material is broken upand removed to a slag processing facility, where relatively large chunksof iron and slag are broken down into substantially smaller blastfurnace slag iron pieces, such as by the use of a wrecking ball.

In a typical example, a wrecking ball weighing at least 15 tons would bedropped onto the pieces of iron and slag from a height of at least feet.This process shatters the slag into a large number of small pieces, fromwhich the ironcontaining blast furnace slag iron pieces may be separatedby the use of a suitable electromagnet which can be adjusted to separateout only pieces having a predetermined amount of iron. Therefore,although the slag pit contains a predominant amount of slag and arelatively minor amount of iron (2 to 5 percent), the blast furnace slagiron pieces which are removed at the slag processing facility willcomprise only those pieces having some significant amount of iron. Thepieces which are utilized in the process of this invention willdesirably have sizes of up to approximately 2 or 3 feet in maximumdimension, any larger pieces being impacted again with the wreckingball, to reduce their size to a suitable handleable size. The maximumsize of these pieces is determined by the size of piece that can becharged into and efficiently processed in, a shot blasting machine andsubsequently accommodated in a melting furnace.

These blast furnace slag iron pieces, having maximum dimensions of up to2 or 3 feet, are then transported, as by conveyor, truck, or railroadcar to the final processing facility.

FIG. 1 illustrates schematically one form of tumbling and shot blastingmachine usable in the process of this invention, which is commerciallyavailable. One suitable such tumbling and shot blasting machine is soldby Wheelabrator-Frye Inc. under the Super-Tumblast trademark. Thesemachines, which come in different sizes and capacities, essentiallycomprise an enclosed chamber in which a given quantity of material ischarged, and in which the mass of pieces is tumbled while it is impactedby a recirculating, high velocity continuous stream of pellets of shotor grit, which are discharged downwardly onto the mass of rotatingpieces.

Viewing FIG. 1, the tumbling and shot blasting machine, which isgenerally designated by numeral 20, is seen to comprise a housing 22inwhich is formed an enclosure 24 into which the pieces to be worked onare charged. Enclosure 24 has a door 29 which can be opened forinserting and removing the pieces 10, and which is closed during theactual tumbling and shot blasting operation. Located within enclosure 24is conveyor 26, which is an L-shaped conveyor, comprising individualmetal slats 28, each of which has a plurality of circular apertures 30.Each of the apertures 30 has a diameter of approximately five-eighthsinch. The conveyor 26 is mounted for counterclockwise movement, duringthe shot blasting step, on a plurality of drive wheels 36 which aredriven by a suitable drive motor (not shown). The conveyor direction isreversed to discharge finished product from the shot blasting machine.

The conveyor 26 has a vertical section and a horizontal section, formingan L shape. When the pieces 10 to be treated are loaded into enclosure24, they are placed on top of the horizontal surface of the conveyor 26.The drive motor for conveyor 26 may be reversible, so that it may bereversed to facilitate discharge of the finished pieces when door 29 isopened. A typical drive speed for conveyor 26 is feet per minute.

Located in the upper portion of the housing are one or two rotatablymounted thrust members 32 called throwing wheels or impellers, thepurpose of which is continuously to deliver large quantities of shot orgrit. at high velocity, against the upper face of the mass of pieces 10located in enclosure 24. For simplicity, only one throwing wheel isillustrated, but, if two wheels are utilized, as is preferred, bothwheels are of the same size and the two wheels are parallel. The twothrowing wheels 32 are, in a preferred embodiment of the invention,rotated at approximately 3,600 rpm, and are each 15 inches in diameter.The two wheels 32 may each be driven by a motor (not shown) of about 60to about 75 horsepower, and each imparts to the shot a tangentialvelocity of approximately 19,000 feet per minute. The throwing wheelswill preferably deliver in the range from about 2,000 to about 4,000pounds of shot per minute, if an enclosure 24 having a capacity tohandle about 50 cubic feet of slag iron pieces 10 is used. The design ofthe throwing wheels and their details are well known.

As illustrated in FIG. 1, the shot is generally designated by numeral 34and preferably comprises small, hard spherical balls, more fullydescribed below.

It is important to note that, for optimum operating efficiency, theenclosure 24 is filled with pieces 10 only to a level of aboutfour-tenths of the total height of the enclosure, thus occupying about40 percent of the enclosure volume. It is this optimum volume which isoccupied which is used to designate the machine capacity. Thus a 50cubic foot machine contains material occupying 50 cubic feet, when it isforty percent filled. This design capacity is selected to give theoptimum efficiency of the shot blasting operation, and other volumes maybe used, but with less efficiency.

The shot 34 impacts the upper surfaces of the mass of blast furnace slagiron pieces 10 and, because of the substantial hardness and kineticenergy of the shot, abrades away the slag 14 in small pieces, generallyon the order of less than several hundredths of an inch in size. Also,some larger pieces of slag are broken away from the pieces 10 by virtueof the impact of the various pieces 10 against each other as they aretumbled about enclosure 24 because of the movement of conveyor 26.

The movement of conveyor 26 effects a continuous tumbling movement andredistribution of the pieces 10 within enclosure 24, so that differentpieces and different surfaces of each piece are continuously exposed tothe direct impact of the high velocity shot 34, thereby to effect auniform abrasion of the slag from the iron or other metal to berecovered. After each piece of shot impacts one or more pieces 10, itpasses downwardly through the mass of those pieces to the conveyor 26,where the movement of the pieces 10 on the conveyor 26 causes a flow ofthe individual shot members. The pieces of shot exit the enclosure 24 bypassing downwardly through apertures 30 in the slats 28 of conveyor 26.The apertures 30 are approximately five-eighths of an inch in diameter,and will also, therefore, pass appropriately small pieces of slag, andoccasional small pieces of iron which may also be abraded in theenclosure 24. These small pieces of shot, slag and iron, all of whichare necessarily less than five-eighths inch in maximum dimension, passthrough the apertures 30 in the slats 28 and fall into enclosure 40 inthe bottom of the unit 20, where they are transported by conveyor screw38.

The conveyor 38 may be a screw conveyor or a shaking conveyor, whichtransports the combination of shot, slag and iron across a screen offit-inch mesh (not shown). The particles which are greater thanonequarter inch in size remain on the screen, and constitute mostly slagparticles and some iron. These particles are then passed, by a suitableconveyor (not shown), past a magnetic separator, which recovers thehighly magnetic materials, comprising both iron and slag, but havingenough iron to merit recovery for subsequent recovery and reuse. Theparticles which are less than one-fourth inch in diameter, comprisingall of the shot, most of the slag particles generated by the shotblasting operation and some iron particles, drop freely verticallythrough the screen and are conveyed by bucket elevator 42 and screwconveyor 46 to an air separator (not shown) where the cascading streamof particles is contacted by a high velocity air stream. This airseparator is located in the upper chamber 48. Because the slag is ofsubstantially lower density than the shot (or grit), it is blown furtheraway by the air stream and is blown into a ducting system (not shown)which transports the slag to a bag house. The heavier shot and smallerslag iron pieces are not blown as far as the larger slag pieces, andthey fall into shot hoppers (not shown) in chamber 48. These shothoppers have adjustable discharge openings, and they function to keepthe throwing wheels loaded with shot.

It is notable that the slag particles which pass through the screen,having a Ar-inch or less size, as well as the very fine slag collectedin the bag house, could be used as a component of certain types ofcement which normally incorporate blast furnace slag therein.

It is to be noted that the structural details of the tumbling and shotblasting mechanism 20 are well known in the art and form no part of thisinvention. In the most preferable embodiment of the invention, thetumbling and shot blasting unit is of at least 50 cubic foot size, thatis to say, the optimum working capacity of enclosure 24 is 50 cubicfeet.

In the operation of the process of this invention, it is first necessaryto reduce the slag iron pieces to usable sizes of up to approximately 2or 3 feet in maximum dimensions. A substantial number of these pieces,typically comprising a charge weighing about 5,500 to 6,000 pounds, whena 50 cubic foot enclosure 24 is used, are then placed in a suitabletumbling and shot blasting mechanism 20 for the purpose of providing arelatively continuous tumbling and agitation of the individual pieces.

The individual pieces are then subjected to the impact of a highvelocity stream of small spherical steel shot or hard grit 34, having aflow rate in the range from about 2,000 to about 4,000 pounds per minuteand a hardness which is substantially greater than the hardness of theslag and having a size which is in the range of up to about one-tenth ofan inch, and is preferably in the range from approximately 0.025 inchesto approximately 0.060 inches for a period in the range from about 10 toabout 60 minutes. It has been found that the smaller particles,preferably about 0.039 inches nominal size, provide a more effectivecleaning, in that they are better able to penetrate deeply into anycrevices and fissures in the blast furnace slag iron pieces. It is to benoted that when shot is sold the individual particles usually cover arange of sizes around the specification size. Therefore, if 0.039 inchshot is specified, some of the pieces supplied will be somewhat lessthan 0.039 inches in diameter and some slightly greater than that size.

It is also notable that there are approximately 400,000 shot pellets perpound, if a 0.039 inch diameter steel shot is used, and that this woulddesirably produce a flow rate of approximately 3,000 pounds per minuteusing two 15 inch diameter throwing wheels 32, each driven by a 75horsepower motor. The shot consists of a high carbon steel alloyed withchromium, having about 1 percent carbon, and having a hardness ofapproximately 48 on the Rockwell C scale. A desirable shot having thesecharacteristics is sold by Wheelabrator-Frye Inc. under the designationS390.

The velocity imparted to the shot or grit and its flow rate may bevaried within wide ranges, and the precise velocity and flow rateutilized will depend upon the size of the available drive motor for thethrowing wheel and the time period within which it is desired to cleanthe slag from the iron. Desirably, the velocity imparted to the shot orgrit, for a 50 cubic foot volume of charge, will be in the range fromapproximately 10,000 to approximately 35,000 feet per minute, leavingthe throwing wheel. It is most preferred to impart a velocity ofapproximately 19,000 feet per minute at the throwing wheel, whenutilizing a 50 cubic foot machine. TI-Ie optimum flow rate for a 50cubic foot charge would be about 3,000 pounds per minute.

EXAMPLE I Approximately 20,000 pounds of blast furnace slag iron havingsizes of up to 2 or 3 feet in maximum dimensions and thicknesses of upto about 6 inches, were processed using the method of this invention.The machine utilized for the processing was a 50 cubic foot WheelabratorSuper-Tumblast, having two 60 horsepower throwing wheels and utilizingsteel shot having a 0.055 inch nominal diameter, and designated as 8-550shot. This machine imparts approximately 19,000 feet per minute oflinear velocity to the steel shot at the point of departure from thethrowing wheel at a flow rate of about 2,400 pounds per minute. Theconveyor 26 was set at an operating speed of approximately 15 linearfeet per minute.

In one instance, the enclosure was loaded with approximately 4,200pounds of the slag iron pieces, and in each of two other instances itwas loaded with approximately 7,500 pounds of the slag iron pieces. The

4,200 pound batch was processed for 15 minutes, one of the 7,500 poundbatches was processed for 25 minutes, and the other was processed for 40minutes.

The 4,200 pound batch was inspected at various stages during the 15minute blast period. After 5 minutes of processing, cleaning was wellunder way, but the product was not yet satisfactory. After minutes, theproduct was judged to be at least 90 percent metallic, and after minutesthe material was at least 96 to 97 percent metallic.

The two 7,500 pound batches constituted grossly overloaded conditionsfor the 50 cubic foot Super- Tumblast, which really should not becharged with more than 5,500 to 6,000 pounds of slag iron for efficientprocessing. It was a matter of practical interest, however, to observejust how well the machine would do under these conditions.

With the first 7,500 pound test, 15 minutes of processing gave goodresults, but the percentage of metallics was not as high as it was inthe case of the 4,200 pound batch after the same blasting time. This wasto be expected, because in the case of the 7,500 pound load, the piecesdid not receive the degree of exposure to the shot that they received inthe 4,200 pound load. After a total of 25 minutes of processing, thisload had been cleaned of slag up to the same percentage of metallics aswas observed after 15 minutes of processing with the 4,200 pound batch.

In the second 7,500 pound test, the material was inspected after 30minutes of processing, and it was found to be at least 96 percentmetallic. After 40 min utes of processing, the product was at least 98percent metallic.

EXAMPLE II A different 50 cubic foot Super-Tumblast unit was employedfor a second series of tests. It was decided that, although theequipment performs rather well when overloaded, it is better to chargethe machine with no more than the recommended 50 cubic feet of slagiron, which weighed about 5,700 to 6,000 pounds.

The only other significant difference in the test conditions betweenExample I and II was that in Example II, the shot diameter was 0.039inches, compared to 0.055 inches in Example I.

Four tests were conducted for this Example, in order to prepare materialof varying cleanliness (freedom from slag) by varying the length of theprocessing time. One load was processed for 20 minutes, one for 30minutes, and two for 40 minutes.

The results of the 30 and 40 minute processing cycles were excellent; atleast 98 percent metallics had been achieved in all three tests.Essentially 95 percent metallics was reached in the 20 minuteprocessing.

Generally speaking, the results of the second series of tests weresuperior to those of the first. This conclusion is attributed mainly tothe smaller shot diameter, which apparently penetrated the crevices ofthe pieces more thoroughly than did the coarser shot of the firstseries.

It is notable that the process of this invention is equally applicableto the steel metallics magnetically extracted from the slag produced bybasic oxygen furnaces, open hearth furnaces, and electric arc furnaces,and to iron metallics recovered from various foundry melting slags.

The product of this invention is a body of a relatively high puritymetal, which may be blast furnace iron,

steel, aluminum, zinc. copper or the likev The product has an irregularsurface having a substantial number of crevices and fissures. which arefree of slag. the total slag content of each piece being no more thanabout percent by weight and preferably being no more than about 2percent by weight.

The iron product of this invention can be used in all forms of steelmaking. That is to say, the cleaned blast furnace iron can be used inmaking steel by any process, as well as in making iron castings. as asubstitute for the cast iron scrap and pig iron normally used in makingiron castings. The ultimate composition of the product of this inventionwould most desirably be no less than about 98 percent iron and no morethan 2 percent slag, and have a total of no more than up toapproximately 0.05 percent by weight of sulfur. It is to be noted thatthis is to be compared with conventional blast furnace iron which has upto about approximately 0.05 percent sulfur maximum, and the slag fromthe blast furnace which has up to approximately 2 percent by weight ofsulfur. The reason why the sulfur content of the cleaned blast furnaceiron produced by this process is about 0.05 percent or less,notwithstanding the relatively high sulfur content of the slag. isbecause the amount of slag is so low as to be virtually insignificant asa sulfur contributor.

It is notable that the process of this invention can be varied withinreasonable limits without departing from the spirit and scope of theinvention. For example. the particular hardness, size and shape of theshot or grit used, the velocity imparted thereto and the flow ratethereof. the linear speed of the conveyor. and the precise size andquantity of the metalslag pieces. as well as the time during which theprocess is applied. can be varied without departing from the spirit andscope of the invention.

It is also notable that the process of this invention may be used totreat aluminum. brass. copper or other metals to remove slag from thecrevices and fissures thereof.

What is claimed is:

1. A process for recovering a relatively pure metal having a slagcontent not exceeding 10 percent by weight from a piece of such metalcontaining a softer slag impurity rigidly adhered thereto and located atleast in substantial part within crevices and fissures accessible to thesurface of said metal. comprising:

a. Breaking said metal containing impurities into pieces having asubstantial amount of such slag impurities exposed at or to the surfaceof each piece;

b. Continuously tumbling a mass of such pieces against each other inorder to achieve a relatively uniform redistribution of such pieceswithin such mass; and c. While effecting such redistribution.substantially continuously impacting such pieces with a shower of asubstantial quantity of small particles having a hardness greater thanthe hardness of the slag impurities and at a high velocity of at leastabout 10,000 feet per minute. and for a period of time sufficient toabrade such impurities from the metal to produce a product containingnot more than 10 percent by weight of said slag impurities.

2. A process as set forth in claim 1. wherein said metal is blastfurnace iron having a sulfur content of up to about 0.05 percent byweight and said impurity is iron slag having a sulfur content of up toabout 2 percent by weight.

3. A process as set forth in claim 1, wherein said particles have avelocity in the range from about 10.000 feet per minute to about 20.000feet per minute. and a feed rate in the range from about 2.000 to about4,000 pounds per minute based on the processing of a mass occupyingabout cubic feet.

4. A process as set forth in claim 1. wherein said steps (b) and (c)occupy a period in the range from about 10 to about minutes and saidproduct contains no more than 3 percent by weight of said impurities.

5. A process as set forth in claim 1, wherein said pieces are tumbled ona conveyor having a speed of about 15 feet per minute.

6. A process as set forth in claim 1. wherein said metal is blastfurnace iron and said impurity is iron slag and said particles are steelshot or grit having an average size of about 0.39 inches. a velocity ofabout 19.000 feet per minute and a flow rate in the rate from about2.000 to about 4.000 pounds per minute based on the processing of a massoccupying about 50 cubic feet.

7. A process as set forth in claim 6. wherein said steps (b) and (c)occupy a time period in the range from about 15 to about 40 minutes andsaid product contains no more than 5 percent by weight of saidimpurities.

8. A process as set forth in claim 1, wherein said metal is steel.

9. The product of the process of claim 1.

10. The product of the process of claim 6.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,3,997 Dated Maw 20. 1975 l e t Richard D. Burlingame It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 22, change "or" to --of.

Column 5, line +2, after "2" first occurrence, insert --feet--.

Column 5, line 6Q, change "amount" to --amounts--.

Column 6, line 25, change "ironcontaining" to --iron-containing.

Signed and Emalcd this sixteenth D ay Of December 1 9 75 [SEAL] A ttest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ojlatentsand Trademarks

1. A PROCESS FOR RECOVERING A RELATIVELY PURE METAL HAVING A SLAGCONTENT NOT EXCEEDING 10 PERCENT BY WEIGHT FORM A PIECE OF SUCH METALCINTAINING A SOFTER SLAG IMPIRITY RIGIDLY ADHERED THERETO AND LOCATED ATLEAST IN SUBSTANTIAL PART WITHIN CREVICES AND FISSURES ACCESSIBLE TO THESURFACE OF SAID METAL, COMPRISING: A. BREAKING SAID METAL CONTAININGIMPURITIES INTO PIECES HAVING A SUBSTANTIAL AMOUNT OF SUCH SLAGIMPURITIES EXPOSED AT OR TO THE SURFACE OF EACH PIECE; B. CONTINUOUSLYTUMBLING A MASS OF SUCH PIECES AGAINST EACH OTHER IN ORDER TO ACHIEVE ARELATIVELY UNIFORM REDISTRIBUTION OF SUCH PIECES WITHIN SUCH MASS; ANDC. WHILE EFFECTING SUCH REDISTRIBUTION, SUBSTANTIALLY CONTINUOUSLYIMPACTING SUCH PIECES WITH A SHOWER OF A SUBSTANTIAL QUANTITY OF SMALLPARTICLES HAVING A HARDNESS GREATER THAN THE HARDNESS OF THE SLAGIMPURITIES AND AT A HIGH VELOCITY OF AT LEAST ABOUT 10,000 FEET PERMINUTE, AND FOR A PERIOD OF TIME SUFFICIENT TO AVRADE SUCH INPURITIESFROM THE METAL TO PRODUCE A PRODUCT CONTAINING NOT MORE THAN 10 PERCENTBY WEIGHT OF SAID SLAG IMPURITIES.
 2. A process as set forth in claim 1,wherein said metal is blast furnace iron having a sulfur content of upto about 0.05 percent by weight and said impurity is iron slag having asulfur content of up to about 2 percent by weight.
 3. A process as setforth in claim 1, wherein said particles have a velocity in the rangefrom about 10,000 feet per minute to about 20,000 feet per minute, and afeed rate in the range from about 2,000 to about 4,000 pounds per minutebased on the processing of a mass occupying about 50 cubic feet.
 4. Aprocess as set forth in claim 1, wherein said steps (b) and (c) occupy aperiod in the range from about 10 to about 60 minutes and said productcontains no more than 3 percent by weight of said impurities.
 5. Aprocess as set forth in claim 1, wherein said pieces are tumbled on aconveyor having a speed of about 15 feet per minute.
 6. A process as setforth in claim 1, wherein said metal is blast furnace iron and saidimpurity is iron slag and said particles are steel shot or grit havingan average size of about 0.39 inches, a velocity of about 19,000 feetper minute and a flow rate in the rate from about 2,000 to about 4,000pounds per minute based on the processing of a mass occupying about 50cubic feet.
 7. A process as set forth in claim 6, wherein said steps (b)and (c) occupy a time period in the range from about 15 to about 40minutes and said product contains no more than 5 percent by weight ofsaid impurities.
 8. A process as set forth in claim 1, wherein saidmetal is steel.
 9. The product of the process of claim
 1. 10. Theproduct of the process of claim 6.